The thyrotropin receptor (TSHR) plays a vital role in thyroid physiology and pathophysiology. Physiologically, the TSHR is a partner in the thyroid hormone servo-feedback loop on pituitary TSH secretion. In Graves'disease thyroid-stimulating autoantibodies (TSAb) activate the TSHR and cause hyperthyroidism. Understanding how TSAb and TSH interact with the TSHR extracellular domain and how the TSHR structure predisposes to TSAb generation are important clinical goals. The TSHR, like the other glycoprotein hormone receptors, is a member of the G protein-coupled receptor superfamily with a very large ectodomain consistent with the large size of its ligand, TSH. The TSHR receptor ectodomain comprise three components:- 7 A cysteine-rich N-terminal domain (NTD;amino acid residues 22-41 after deletion of the signal peptide). Although containing two anti-parallel leucine-rich repeats, it has some distinctive features that permits it to be considered separately from the following component. 7 A leucine-rich repeat domain (LRD) forming a slightly curved tubular structure. Each repeat has a beta-strand on its concave surface that forms part of the TSH binding region. 7 A hinge region (approximately amino acid residues 270-412) linking the LRD to the insertion of the ectodomain into the plasma membrane. The hinge region is also unique among the glycoprotein hormone receptors in containing a ~50 amino acid segment that is deleted during intramolecular cleavage into disulfide-linked A- and B-subunits. Most is known about the TSHR LRD, whose crystal structure has been determined. However the structure of its NTD component has not been fully defined. We will continue our studies on the TSHR NTD based on our evidence that it plays a role in TSAb function, and also possibly in the generation of TSAb leading to Graves'disease. The structure of the hinge region is entirely unknown yet is vital to understanding TSHR structure and function. Although neglected by most investigators, there is evidence that the TSHR hinge region contains part of the TSH binding site, couples TSH binding with signal transduction and influences ligand-independent constitutive activity. The hinge must also stabilize the position of the LRD relative to the membrane spanning TMD. The proposed studies on the least well understood TSHR NTD and hinge regions will provide novel insight into the structure and function of the TSH holoreceptor and its activation by TSH and TSAb in Graves'disease.

Public Health Relevance

PROJECT NARRATIVE The thyrotropin receptor (TSHR) plays a vital role in thyroid physiology and pathophysiology. Physiologically, the TSHR is a partner in the thyroid hormone servo-feedback loop on pituitary TSH secretion. In Graves'disease thyroid-stimulating autoantibodies (TSAb) activate the TSHR and cause hyperthyroidism. We will continue our studies to provide further mechanistic insight into how TSAb and TSH interact with the TSHR extracellular domain and activate the receptor.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Research Project (R01)
Project #
5R01DK019289-37
Application #
8236976
Study Section
Integrative and Clinical Endocrinology and Reproduction Study Section (ICER)
Program Officer
Spain, Lisa M
Project Start
1976-05-01
Project End
2015-05-31
Budget Start
2012-06-01
Budget End
2013-05-31
Support Year
37
Fiscal Year
2012
Total Cost
$396,000
Indirect Cost
$156,000
Name
Cedars-Sinai Medical Center
Department
Type
DUNS #
075307785
City
Los Angeles
State
CA
Country
United States
Zip Code
90048
Rapoport, Basil; McLachlan, Sandra M (2014) Graves' hyperthyroidism is antibody-mediated but is predominantly a Th1-type cytokine disease. J Clin Endocrinol Metab 99:4060-1
McLachlan, Sandra M; Rapoport, Basil (2014) Breaking tolerance to thyroid antigens: changing concepts in thyroid autoimmunity. Endocr Rev 35:59-105
Hamidi, Sepehr; Chen, Chun-Rong; Murali, Ramachandran et al. (2013) Probing structural variability at the N terminus of the TSH receptor with a murine monoclonal antibody that distinguishes between two receptor conformational forms. Endocrinology 154:562-71
McLachlan, Sandra M; Rapoport, Basil (2013) Thyrotropin-blocking autoantibodies and thyroid-stimulating autoantibodies: potential mechanisms involved in the pendulum swinging from hypothyroidism to hyperthyroidism or vice versa. Thyroid 23:14-24
Chen, Chun-Rong; Salazar, Larry M; McLachlan, Sandra M et al. (2012) Novel information on the epitope of an inverse agonist monoclonal antibody provides insight into the structure of the TSH receptor. PLoS One 7:e31973
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McLachlan, Sandra M; Lu, Lu; Aliesky, Holly A et al. (2011) Distinct genetic signatures for variability in total and free serum thyroxine levels in four sets of recombinant inbred mice. Endocrinology 152:1172-9
Hamidi, Sepehr; Chen, Chun-Rong; Mizutori-Sasai, Yumiko et al. (2011) Relationship between thyrotropin receptor hinge region proteolytic posttranslational modification and receptor physiological function. Mol Endocrinol 25:184-94
McLachlan, Sandra M; Aliesky, Holly A; Chen, Chun-Rong et al. (2011) Exceptional hyperthyroidism and a role for both major histocompatibility class I and class II genes in a murine model of Graves' disease. PLoS One 6:e21378
Chen, Chun-Rong; Aliesky, Holly A; Rapoport, Basil et al. (2011) An attempt to induce "Graves' disease of the gonads" by immunizing mice with the luteinizing hormone receptor provides insight into breaking tolerance to self-antigens. Thyroid 21:773-81

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